Reinforcing layers for reinforcing the rubber used to form rubber products are embedded in rubber products such as tires, conveyor belts, and rubber hoses. Steel cords constituted by steel wires intertwined together are used as reinforcing members which constitute reinforcing layers. The structures of steel cords vary, but there is a known strand structure which, for example, has a plurality of sheath strands intertwined around the outer circumferential surface of a core strand (specifically, see Japanese Unexamined Patent Application Publication No. 2012-036539A). To manufacture these rubber products, a reinforcing layer formed from a plurality of steel cords extending side by side in parallel is embedded in an unvulcanized rubber member to form a molded article. Thereafter, the molded article is heated at a predetermined temperature and pressurized at a predetermined pressure in a vulcanization process to vulcanize the unvulcanized rubber. Thus, a rubber product in which a reinforcing layer composed of steel cords is embedded is completed.
In recent years, there has been an increasing awareness of energy conservation, and the demand for energy conservation in rubber products has intensified as a result. For example, when a rubber product is reduced in weight, the energy required to transport and use the rubber product can be reduced. Alternatively, when a rubber product is reduced in thickness, this contributes to a reduction in weight and also enables a reduction in vulcanization time, which makes it possible to reduce the energy required for manufacture.
Therefore, reducing the weight and thickness of a reinforcing layer makes it possible to achieve energy conservation. However, when a reinforcing layer is simply reduced in weight and thickness, there is a problem in that the original reinforcing function of the reinforcing layer is diminished.